The instant application should be granted the priority dates of Jan. 28, 2006, the filing date of the corresponding German patent application 10 2006 004 069.4, as well as Jan. 26, 2007, the filing date of the International patent application PCT/EP2007/000688.
The present invention relates to a method of mixing at least one gaseous fluid stream with a large gas stream, especially for introducing a reducing agent into a flue gas that contains nitrogen oxides, whereby the large gas stream flows against at least one disk-like mixer element on an inlet side (windward side) thereof, wherein the mixer element is inclined at an angle counter to the direction of flow, and wherein eddy-type whirls form at the mixer element, further according to which the fluid stream is guided essentially to the center of an impact surface that is associated with the discharge side (lee side) of the mixer element, and according to which the gaseous fluid stream is admixed with the large gas stream.
EP 1 604 742 A1 discloses a method in conjunction with electric filters for the dust separation of large gas streams, according to which the flow whirl, which is formed at the inclined mixer disk, is designated as a leading edge whirl. The edge of the preferably circular disk that is directed against the large gas stream is designated as the intake edge, the other edge is designated as the breaking edge. These are not linear edges, but rather curved edges.
The vertical wall of the gas duct that guides the large gas stream has a short section of pipe for the admixture of a conditioning fluid pass perpendicularly therethrough. The short pipe section opens out, as viewed in the direction of flow of the large gas stream, behind the intake edge of the mixer disk without overlapping the mixer disk. The conditioning agent stream that exits the short pipe section strikes the edge-continuous partial surface of the discharge side of the mixer disk, adjacent to the section outlet, at an angle that corresponds to the angle of inclination of the disk relative to the direction of flow of the large gas stream. Column 6, lines 5-6, of EP 1 604 742 A1 indicates that methods are also expedient according to which the admixture device is mounted directly on the whirl apparatus.
EP 1 568 410 A1 discloses a method of the aforementioned general type for the admixture of fluid streams in conjunction with units for the reduction of the NOx level of a flue gas, according to which the reducing agent that is discharged from the short pipe section strikes the back side of the inclined mixer disk (lee side) close to its central region at an angle that corresponds to the angle of inclination of the disk relative to the direction of flow of the large gas stream. According to column 2, lines 17-20, the short pipe section should extend inwardly over only a short distance beyond the wall of the duct that guides the large gas stream (flue gas). Due to the inclined position of the short section relative to the mixer element, there is no uniform distribution of the gaseous fluid over the entire discharge side (lee side) and the gaseous fluid is not mixed into the flue gas stream over the entire peripheral edge of the mixer element, but rather essentially only over the upper edge portion in FIG. 1 of EP 1 568 410 A1.
With these procedures, there is thus no optimum distribution of the conditioning or reducing agent on the mixer disk, and there is thus no optimum mixing into the whirl system that results at the mixer disk.
With the mixing device described in EP 1 166 861 B1, in conjunction with Denox units and electric filters, the mixer disk (built-in surface) has a chamber into which leads a separate flow channel for the gas that is to be admixed or for another Newtonian fluid, and which serves as a distribution chamber for the gas stream. The chamber is provided on the back side (discharge side; lee side) of the mixer disk that faces away from the in-flow of the large gas stream with discharge openings, and is disposed in the region of the intake edge. Adjoining the distribution chamber toward the breaking edge are chambers that, however, have no distribution function nor a flow-related function, but rather serve exclusively for the reinforcement of the mixer disk. The discharge openings can be formed in the cover of the distribution chamber or in the side wall thereof. However, they can also be formed in an additional hood that is placed upon the chamber. It is furthermore possible that the chamber itself not be provided with a cover that is parallel to the mixer disk, but rather itself have a hood-shaped configuration. The flow channel for the supply of gas can enter into the chamber from the windward side of the mixer disk through the disk, or can be guided to the distribution chamber on the lee side of the mixer disk. With the method described in EP 1 166 861 B1 an additional chamber is required and the mixing-in is again effected only in the vicinity of the intake edge.
Such methods, designated as mixing methods having a static mixer, are, for example, also used with SCR units, to reduce the NOx level (Selective Catalytic Reduction) of flue gases, for example of power plant furnaces, by means of reducing agent and catalyzer. In this connection, it is customary, where the reducing agent is NH3, that it is stored in the form of pressure-condensed NH3 or of ammonium hydroxide (NH4OH), and pre-vaporized NH3 is sprayed into the flue gas stream via a carrier gas stream and is mixed with the flue gas stream. Where the reducing agent is urea, first an aqueous urea solution is produced that, after suitable processing, is then sprayed into the flue gas stream in gaseous form.
The methods are furthermore used, for example, for industrial chimneys, spray driers (see e.g. EP 0 637 726 B1), heat exchangers, flue desulfurization units, and hybrid cooling towers.
It is an object of the present invention, for methods of the aforementioned general type, to improve the mixing of the gaseous fluid stream into the large gas stream.